MATERIALS AND SYSTEMS

Transcription

2
PART
CHAPTER 11
Materials for Wood
Construction–I (Lumber)
CHAPTER 12
Materials for Wood
Construction–II (Manufactured
Wood Products, Fasteners and
Connectors)
CHAPTER 23
Masonry Materials–II
(Concrete Masonry Units,
Natural Stone and Glass
Masonry Units)
CHAPTER 24
Masonry and Concrete Bearing
Wall Construction
CHAPTER 13
Wood Light Frame
Construction–I
CHAPTER 25
Rainwater Infiltration Control
in Exterior Walls
CHAPTER 14
Wood Light Frame
Construction–II
CHAPTER 26
CHAPTER 15
Structural Insulated Panel
System
Exterior Wall Cladding–I
(Masonry, Precast Concrete,
GFRC and Prefabricated
Masonry)
CHAPTER 16
The Material Steel and
Structural Steel Construction
CHAPTER 27
Exterior Wall Cladding–II
(Stucco, EIFS, Natural Stone
and Insulated Metal Panels)
CHAPTER 17
Light-Gauge Steel Construction
CHAPTER 28
CHAPTER 18
Lime, Portland Cement and
Concrete
Transparent Materials (Glass
and Light-Transmitting
Plastics)
CHAPTER 19
Concrete Construction–I
(Formwork, Reinforcement and
Slabs-on-Ground)
CHAPTER 29
Windows and Doors
CHAPTER 30
Glass-Aluminum Wall Systems
CHAPTER 31
Roofing–I (Low-Slope Roofs)
CHAPTER 32
Roofing–II (Steep Roofs)
CHAPTER 33
Stairs
CHAPTER 34
Floor Coverings
CHAPTER 35
Ceilings
CHAPTER 20
Concrete Construction–II
(Sitecast and Precast Concrete
Framing Systems)
CHAPTER 21
Soils, Foundation and
Basement Construction
CHAPTER 22
Masonry Materials–I (Mortar
and Brick)
26
CHAPTER
Exterior Wall
Cladding–I (Masonry,
Precast Concrete, GFRC,
and Prefabricated Masonry)
CHAPTER OUTLINE
26.1 MASONRY VENEER WALL ASSEMBLY—GENERAL CONSIDERATIONS
26.2 BRICK VENEER wITH A CMU OR CONCRETE BACKUP WALL
26.3 BRICK VENEER WITH A STEEL STUD BACKUP WALL
26.4 CMU BACKUP VERSUS STEEL STUD BACKUP
26.5 AESTHETICS OF BRICK VENEER
26.6 PRECAST CONCRETE (PC) CURTAIN WALL
26.7 CONNECTING THE PC CURTAIN WALL TO A STRUCTURE
26.8 BRICK AND STONE-FACED PC CURTAIN WALL
26.9 DETAILING A PC CURTAIN WALL
26.10 GLASS FIBER–REINFORCED CONCRETE (GFRC) CURTAIN WALL
26.11 FABRICATION OF GFRC PANELS
26.12 DETAILING A GFRC CURTAIN WALL
26.13 PREFABRICATED BRICK CURTAIN WALL
Brick veneer buildings, illustrating one of the most widely
used cladding systems in contemporary US construction,
line this New York City street. Note glass-clad Bloomberg
Tower (by Cesar Pelli and Associates with Schuman,
Lichtenstein, Claman and Effron) in the background.
(Courtesy of Emporis.)
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PART 2
This is the first of the two chapters on exterior wall finishes, it includes masonry veneer,
precast concrete, glass fiber–reinforced concrete (GFRC), and prefabricated masonry panels.
Other exterior wall finishes—stucco, exterior insulation and finish systems (EIFS), stone
cladding, and insulated metal panel walls—are discussed in the next chapter.
26.1 MASONRY VENEER ASSEMBLY—GENERAL
CONSIDERATIONS
Among the most commonly used veneer walls is a single wythe of brick (generally 4 in.
nominal thickness), referred to as brick veneer. The backup wall used with brick veneer may
be load bearing or non–load bearing and may consist of one of the following:
• Wood or light-gauge steel stud
• Concrete masonry
• Reinforced concrete
A wood stud (or steel stud) load-bearing backup wall, Figure 26.1, is generally used in
low-rise residential construction. Concrete masonry, non–load-bearing steel stud, and reinforced concrete backup walls are generally used in commercial construction. In fact, brick
veneer with concrete masonry backup is the wall assembly of choice for many building
types, such as schools, university campus buildings, and offices.
The popularity of brick veneer lies in its aesthetic appeal and durability. A well-designed
and well-constructed brick veneer wall assembly generally requires little or no maintenance.
The discussion in this chapter refers to brick veneer. It can, however, be extended to include
other (CMU and stone) masonry veneers with little or no change.
Wood stud back-up wall
consisting of drywall interior
finish (over vapor retarder, if
needed)
Air-weather
retarder
CORRUGATED SHEET
STEEL ANCHOR. Anchor is
nailed to studs through airweather retarder and
exterior shea thing and bent
into brick course as the
construction of brick veneer
progresses.
Insulation
CORRUGATED SHEET STEEL
ANCHOR typically used only in
wood stud backed brick veneer
Brick veneer
1 in. air space typical for brick veneer
with corruga ted sheet steel anchors.
A minimum of 2 in. air space required
with other anchors .
Corrugated sheet steel anchor
(also called corrugated tie)
Minimum width = 7/8 in. and minimum
thickness = 0.03 in. excluding thickness
of zinc coating
FIGURE 26.1 Brick veneer with wood stud backup wall. (Photo by MM.)
704
Anchor must allow
differential movement
between veneer and back-up
in vertical direction
F
TO
EN R TO
M
A
E
OV CUL
O M ENDI
N
OR RP
LE R PE
T
T
LI CHO
AN LL
WA
Wall area per anchor
not to exceed 2.67 ft 2
18 in.
18 in.
maximum maximum
An
mo chor m
bac veme ust
k-u nt b allo
p in etw w d
hor een iffer
e
izo
nta venee ntial
l di r an
rec
tio d
n
CHAPTER 26
EXTERIOR WALL CLADDING
Anchor
Back-up wall
Anchor
32 in. maximum
A TYPICAL
TWO-PIECE
ANCHOR
Air space
Masonry veneer
FIGURE 26.2 Adjustability requirements in various directions of a two-piece anchor.
FIGURE 26.3 Anchor spacing should be determined based on the lateral load and the strength
of anchors. However, for a one-piece, corrugated
sheet anchor or a two-piece, adjustable wire
anchor (wire size W1.7), the maximum spacing
allowed is as shown. W1.7 means that the crosssectional area of wire is 0.017 in.2 (Section 18.13).
Anchors are generally staggered, as shown.
A NCHORS
In a brick veneer assembly, the veneer is connected to the backup wall with steel anchors,
which transfer the lateral load from the veneer to the backup wall. In this load transfer, the
anchors are subjected to either axial compression or tension, depending on whether the wall
is subjected to inward or outward pressure.
The anchors must, therefore, have sufficient rigidity and allow little or no movement in
the plane perpendicular to the wall. However, because the veneer and the backup will usually expand or contract at different rates in their own planes, the design of anchors must
accommodate upward-downward and side-to-side movement, Figure 26.2.
Anchors for a brick veneer wall assembly are, therefore, made of two pieces that engage
each other. One piece is secured to the backup, and the other is embedded in the horizontal
mortar joints of the veneer. An adjustable, two-piece anchor should allow the veneer to
move with respect to the backup in the plane of the wall, but not perpendicular to it.
An exception to this requirement is a one-piece sheet steel corrugated anchor
(Figure 26.1). The corrugations in the anchor enhance the bond between the anchor and
the mortar, increasing the anchor’s pullout strength. But the corrugations weaken
This dimension = 2 in. + thickness
the anchor in compression by making it more prone to buckling. A one-piece, corof insulation but not to exceed 4-1/2 in.
rugated anchor is recommended for use only in low-rise, wood, light-frame buildings in low-wind and low-seismic-risk locations.
Galvanized steel is commonly used for anchors, but stainless steel is recom2 in. AIR SPACE
mended where durability is an important consideration and/or where the environment is unusually corrosive.
The spacing of anchors should be calculated based on the lateral load and the
Back-up wall
strength of the anchor. However, the maximum spacing for a one-piece, corrugated
Insulation,
anchor or an adjustable, two-piece wire anchor (wire size W1.7) is limited by the code
if used
2
to one anchor for every 2.67 ft [1]. Additionally, they should not be spaced more
AIR SPACE
than 32 in. on center horizontally and not more than 18 in. vertically, Figure 26.3.
A IR S PACE
An air space of 2 in. (clear) is recommended for brick veneer. Thus, if there is 1 12 -in.thick (rigid) insulation between the backup wall and the veneer, the backup and the
veneer must be spaced 3 12 in. apart so that the air space is 2 in. clear, Figure 26.4.
In a narrower air space, there is a possibility that if the mortar squeezes out into the
air space during brick laying, it may bridge over and make a permanent contact with
the backup wall. A 2-in. air space reduces this possibility. In a wood-stud-backed wall
assembly with one-piece corrugated anchors, however, a 1-in. air space is commonly
used (Figure 26.1).
Veneer
Two-piece
anchor
FIGURE 26.4 A cavity width of 2 in. is recommended, except in low-rise residential buildings, where a 1-in. cavity width is common. The
gap between the veneer and the backup wall
should not exceed 4 12 in.
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PART 2
The maximum distance between the veneer and backup wall is limited by the masonry
code to 4 12 in. unless the anchors are specifically engineered to withstand the compressive
stress caused by the lateral load. With a large gap between the veneer and the backup wall,
the anchors are more prone to buckling failure.
S UPPORT
FOR
B RICK V ENEER —S HELF A NGLES
The dead load of brick veneer may be borne by the wall foundation without any support
at intermediate floors up to a maximum height of 30 ft above ground. Uninterrupted,
foundation-supported veneer is commonly used in a one- to three-story wood or lightgauge steel frame buildings, Figure 26.5(a). In these buildings, the air space is continuous
Air space
Intermediate floor
Mortar - capturing device
Flashing and weep holes
30 ft maximum veneer height
Back-up wall
VENEER EXTENDS
CONTINUOUSLY FROM
FOUNDATION TO ROOF
without any intermediate
support
Spandrel beam
GAP between shelf
angle and top of veneer,
see Figure 26.6
Two-piece anchor
Spandrel beam
Intermediate floor
Back-up wall
Two-piece
anchor
Flashing
and weep holes
Mortar capturing device
Gap between shelf angle
and top of veneer below
allows the spandrel beam
to deflect freely without
transferring the gravity
load to veneer, see Figure
26.6
Two-piece anchor
BRICK LEDGE
Foundation
(a) ENTIRE HEIGHT OF VENEER
SUPPORTED ON FOUNDATION–
a detail generally used in lowrise
buildings
FIGURE 26.5 Dead load support for veneer.
706
SHELF ANGLE
anchored to
spandrel beam,
see Figure 26.20
Finished
ground
SHELF ANGLE
anchored to
spandrel beam, see
Figure 26.20
Gap between spandrel beam
and top of back-up wall allows
the beam to deflect freely
without transferring gravity
load to the back-up wall.
Lateral support to back-up wall
required here. Gap filled with
insulation and treated with
backer rod and sealant
BRICK LEDGE
Foundation
(b) VENEER SUPPORTED AT EACH FLOOR LEVEL
BY SHELF ANGLES.
Air space
Termination bar to fasten flashing to frame
Brick veneer
Flashing
Mortar -capturing device
Weep hole
FIRST COURSE OF BRICK VENEER LAID DIRECTLY
OVER FLASHING AND FLASHING LAID DIRECTLY
OVER SHELF ANGLE
Gap based on the maximum live load
deflection of spandrel beam, brick
veneer's expansion and creep in columns
(if any).
Backer rod and low-modulus
sealant (see Chapter 9)
Structural frame
Shelf angle anchored to
structural frame
Shim between angle and
structural frame (where
needed) to extend full
height of angle leg
FIGURE 26.6 Schematic detail at a typical shelf angle.
from the foundation to the roof level, and the entire load of the veneer bears on the foundation. A 1 21 -in. depression, referred to as the brick ledge, is commonly created in the foundation to receive the first course of the veneer.
In mid- and high-rise buildings, the veneer is generally supported at each floor using
(preferably hot-dip galvanized) steel shelf angles (also referred to as relieving angles). Shelf
angles are supported by, and anchored to, the building’s structure. In a frame structure, the
shelf angles are anchored (welded or bolted) to the spandrel beams, Figure 26.5(b). In a
load-bearing wall structure, the shelf angles are anchored to the exterior walls. The details
of the anchorage of a shelf angle to the structure are given later in the chapter.
A gap should be provided between the top of the veneer and the bottom of the shelf
angle. This gap accounts for the vertical expansion of brick veneer (after construction) and
the deflection of the spandrel beam under live load changes. The gap should be treated with
a backer rod and sealant, Figure 26.6. The veneer may project beyond the shelf angle, but
the projection should not exceed one-third of the thickness of the veneer.
Shelf angles must not be continuous. A maximum length of about 20 ft is used for shelf
angles, with nearly a 38 -in. gap between adjacent lengths to provide for their expansion. The
gap should ideally be at the same location as the vertical expansion joints in the veneer.
NOTE
Brick Ledge
A brick ledge refers to the
depression in concrete foundation at the base of brick
1
veneer and is generally 1 2 in.
deep, because it is formed by
a 2-by lumber used as a blockout when placing concrete
(Figure 26.5). The depression
further prevents water intrusion into the backup wall.
L INTEL A NGLES —L OOSE -L AID
Whether the veneer is supported entirely on the foundation or at each floor, additional dead
load support for the veneer is needed over wall openings. The lintels generally used over an
opening in brick veneer are of steel (preferably hot-dip galvanized) angles, Figure 26.7.
Unlike the shelf angles, lintel angles are not anchored to the building’s structural frame but
are simply placed (loose) on the veneer, Figure 26.8.
To allow the lintel to move horizontally relative to the brick veneer, no mortar should be
placed between the lintel bearing and the brick veneer. Flashing and weep holes must be
provided over lintels in exactly the same way as on the shelf angles.
L OCATIONS
OF
F LASHINGS
AND
E ND DAMS
As shown in Figure 26.7, flashings must be provided at all interruptions in the brick veneer:
•
•
•
•
At foundation level
Over a shelf angle
Over a lintel angle
Under a window sill
Joints between flashings must be sealed, and all flashings must be accompanied by weep
holes. The flashing should preferably project out of the veneer face to ensure that the water
707
PART 2
will drain to the outside of the veneer (Figure 26.6). Where the flashing terminates, it must be
turned up (equal to the height of one brick) to form a dam to prevent water from entering the
air space, Figure 26.9.
F LASHING M ATERIALS
Flashing material must be impervious to water and resistant to puncture, tear, and abrasion.
Additionally, flashing must be flexible so that it can be bent to the required profile.
Durability is also important because replacing failed flashing is cumbersome and expensive.
Therefore, metal flashing must be corrosion resistant. Resistance to ultraviolet radiation is
Back-up wall
Spandrel beam
Shelf angle
FLASHING
AND WEEP
HOLES
Lintel in
back-up wall
LINTEL
ANGLE
Window
FLASHING
AND WEEP
HOLES
Two-piece
anchor
FLASHING
AND WEEP
HOLES
Back-up wall
Spandrel
beam
Shelf angle
FLASHING
AND WEEP
HOLES
Foundation
FIGURE 26.7 A schematic section showing the locations of shelf angles and lintel angles in a typical
brick veneer wall assembly.
708
CHAPTER 26
The back-up wall in this building consists of
metal studs with gypsum sheathing. The
tape covers the joints between sheathing
panels. If an air-weather retarder was used,
taping of joints would be unnecessary.
Lintel angle is simply placed on the veneer
with no anchorage to building's structure.
No mortar bed should be used under lintel
bearing.
Flashing
No mortar
under lintel
angle
Gypsum sheathing joints taped
No mortar between flashing and lintel angle,
see Figure 26.6.
One piece of a
two-piece anchor
Mason cutting the flashing
after turning it over lintel angle
The first course of veneer over flashing is
laid without any mortar bed between bricks
and flashing, see Figure 26.6.
FIGURE 26.8 Lintel angles in a brick
veneer wall. (Photos by MM.)
also necessary because the projecting part of the flashing is exposed to the sun. Commonly
used flashing materials are as follows:
• Stainless sheet steel
• Copper sheet
• Plastics such as
• Polyvinyl chloride (PVC)
• Neoprene
• Ethylene propylene diene monomer (EPDM)
• Composite flashing consisting of
• Rubberized asphalt with cross-laminated polyethylene, typically available as selfadhering and self-healing flashing
• Copper sheet laminated on both sides to asphalt-saturated paper or fiberglass felt
Flashing turned up
to form end dams
FIGURE 26.9 End dams in flashing. (Photo courtesy of Brick Industry Association, Reston, Virginia.)
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PART 2
Open head joint
as a weep hole
FIGURE 26.10 Open head joints as weep holes. (Photo by MM.)
Copper and stainless steel are among the most durable flashing materials. Copper’s advantage over stainless steel is its greater flexibility, which allows it to be bent to shape more easily.
However, copper will stain light colored masonry because of its corrosion, which yields a
greenish protective cover (patina). Copper combination flashing, consisting of a copper
sheet laminated to asphalt-saturated paper, reduces its staining potential.
A fairly successful flashing is a two-part flashing, comprising a self-adhering, self-healing
polymeric membrane and stainless steel drip edge. The durability and rigidity of stainless
steel makes a good drip edge, and the flexible, self-adhering membrane simplifies flashing
installation.
C ONSTRUCTION
NOTE
Weep Hole Spacing
A center-to-center spacing of
24 in. is generally used for
weep holes when open-head
joints are used. A spacing of
16 in. is used with weep holes
consisting of wicks or tubes.
AND
S PACING
OF
W EEP H OLES
Weep holes must be provided immediately above the flashing. There are several different
ways to provide weep holes. The simplest and the most effective weep hole is an open, vertical mortar joint (open-head joint) in the veneer, Figure 26.10.
To prevent insects and debris from lodging in the open-head joint, joint screens may
be used. A joint screen is an L-shaped, sheet metal or plastic element, Figure 26.11(a).
Its vertical leg has louvered openings to let the water out, and the horizontal leg is
embedded into the horizontal mortar joint of the veneer. The joint screen has the same
width as the head joints. An alternative honeycombed plastic joint screen is also available, Figure 26.11(b).
Instead of the open-head joint, wicks or plastic tubes ( 38 -in. diameter) may be used in a
mortared-head joint. Wicks, which consist of cotton ropes, are embedded in head joints,
Brick
(a) Louvered sheet
metal joint screen
Brick
Open head joint here
Brick
Brick
(b) Honeycomb
joint screen
FIGURE 26.11 Two alternative screens used with weep holes consisting of open-head joints.
710
Rope wick
FIGURE 26.12 Wicks as weep holes. (Photos by MM.)
Figure 26.12. They absorb water from the air space by capillary action and drain it to the outside. Their drainage efficiency is low.
Plastic tubes are better than wicks, but they do not function as well as open-head joints.
They are placed in head joints with a rope inside each tube. The ropes are pulled out after
the veneer has been constructed. This ensures that the air spaces of the tubes are not
clogged by mortar droppings.
A sufficient number of weep holes must be provided for the drainage of the air space.
Generally, a weep hole spacing of 24 in. is used with open-head joints; 16-in. spacing is
used with wicks or tubes.
M ORTAR D ROPPINGS IN THE
A IR S PACE —M ORTAR -C APTURING D EVICE
For the air space to function as an effective drainage layer, it is important to minimize mortar droppings in the air space. Excessive buildup of mortar in the air space bridges the space.
Additionally, the weep holes function well only if they are not clogged by mortar droppings. Poor bricklaying practice can result in substantial accumulations of mortar on the
flashing. Care in bricklaying to reduce mortar droppings is therefore essential.
Additional measures must also be incorporated to keep the air space unclogged. An earlier practice was to use a 2-in.-thick bed of pea gravel over the flashing. This provides a
drainage bed that allows the water to percolate to the weep holes.
A better alternative is to use a mortar-capturing device in the air space immediately above
the flashing. This device consists of a mesh made of polymeric strands, which trap the droppings and suspend them permanently above the weep holes, Figure 26.13. The use of a
mortar-capturing device allows water in the air space to percolate freely through mortar
droppings to reach the weep holes.
C ONTINUOUS V ERTICAL E XPANSION J OINTS
IN
B RICK V ENEER
As stated in Section 9.8, brick walls expand after construction. Therefore, a brick veneer
must be provided with continuous vertical expansion joints at intervals, Figure 26.14.
The maximum recommended spacing for vertical expansion joints is 30 ft in the field of
the wall and not more than 10 ft from the wall’s corner [2]. The joints are detailed so that
sealant and backer rods replace mortar joints for the entire length of the continuous vertical
expansion joint, allowing the bricks on both sides of the joint to move while maintaining a
waterproof seal, Figure 26.15. The width of the expansion joint is 38 in. (minimum) to
match the width of the mortar joints.
With vertical expansion joints and the gaps under shelf angles (which function as horizontal expansion joints), a brick veneer essentially consists of individual brick panels that
can expand and contract horizontally and vertically without stressing the backup wall or the
building’s structure.
M ORTAR T YPE
AND
M ORTAR J OINT P ROFILE
Type N mortar is generally specified in all-brick veneer except in seismic zones, where
Type S mortar may be used (see Section 22.2). A concave joint profile yields veneer with
more water resistance (see Section 22.3).
711
(a) Mortar capturing device, as installed in air space
(b) Mortar capturing device with mortar droppings, which allows
the water to find its way to the weep holes even with the droppings.
(c) Image illustrates the relative ineffectiveness
of a bed of pea gravel in air space
FIGURE 26.13 Mortar-capturing device. (Photos courtesy of Mortar Net USA Ltd., producers of The Mortar Net™.)
Air space
Backer rod
Back-up wall
Horizontal joint
under shelf angle
Vertical
expansion joint
Horizontal joint
under shelf angle
Clay brick
Clay brick
Sealant
3/8 in. minimum
FIGURE 26.14 Continuous vertical expansion joints in brick
veneer. Note continuous horizontal joints under shelf angles.
(Photo by MM.)
712
FIGURE 26.15 Detail plan of a vertical expansion joint in
brick veneer. This illustration is the same as Figure 9.23.
PRACTICE
Each question has only one correct answer. Select the choice that best
answers the question.
1.
The backup wall in a brick veneer wall assembly consists of a
a. reinforced concrete wall.
b. CMU wall.
c. wood or steel stud wall.
d. all the above.
e. (b) and (c) only.
2.
In a brick veneer wall assembly, the wind loads are transferred
directly from the veneer to the building’s structure.
a. True
b. False
3.
The anchors used to anchor the brick veneer to the backup wall
are generally two-piece anchors to allow differential movement
between the veneer and the backup
a. in all three principal directions.
b. perpendicular to the plane of the veneer.
c. within the plane of the veneer.
d. none of the above.
4.
The anchors in a brick veneer wall assembly provide
a. gravity load support to both veneer and backup.
b. lateral load support to both veneer and backup.
c. gravity load support to the veneer.
d. lateral load support to the veneer.
5.
The minimum required width of air space between brick veneer
and CMU backup wall is
a. 1 in.
b. 1 21 in.
c. 2 in.
d. 3 in.
e. none of the above.
6.
The minimum width of air space generally used between brick
veneer and wood stud backup wall is
a. 1 in.
b. 11 12 in.
c. 2 in.
d. 2 12 in.
e. 3 in.
7.
A steel angle used to support the weight of brick veneer over an
opening is called a
a. Lintel angle.
b. Shelf angle.
c. Relieving angle.
d. all the above.
e. (a) or (b).
8.
A shelf angle must be anchored to the building’s structural frame.
a. True
b. False
9.
A lintel angle must be anchored to the building’s structural frame.
a. True
b. False
10. In
a.
b.
c.
d.
e.
QUIZ
a multistory building, shelf angles are typically used at
each floor level.
each floor level and at midheight between floors.
at foundation level.
all the above.
(a) and (c).
11. For a brick veneer that bears on the foundation and continues to
the top of the building without any intermediate support, the
maximum veneer height is limited to
a. 40 ft.
b. 35 ft.
c. 30 ft.
d. 25 ft.
e. 20 ft.
12. A shelf angle in a brick veneer assembly must provide
a. gravity load support to the veneer.
b. lateral load support to the veneer.
c. gravity load support to both veneer and backup.
d. lateral load support to both veneer and backup.
13. In
a.
b.
c.
d.
e.
a brick veneer assembly, flashing is required
at foundation level.
over a lintel angle.
over a shelf angle.
under a window sill.
all the above.
14. In
a.
b.
c.
d.
e.
a brick veneer assembly, weep holes are required at
each floor level.
each alternate floor level.
immediately above the flashing.
immediately below the flashing.
2 in. above a flashing.
15. The most efficient weep hole in a brick veneer consists of a
a. Wick.
b. Plastic tube.
c. open head joint.
16. A mortar capturing device in a brick veneer assembly is used
a. at each floor level.
b. at each alternate floor level.
c. immediately above a flashing.
d. immediately below a flashing.
e. 2 in. above a flashing.
17. In a brick veneer assembly, vertical expansion joints should be
provided at a maximum distance of
a. 40 ft in the field of the wall and 40 ft from a wall’s corner.
b. 30 ft in the field of the wall and 30 ft from a wall’s corner.
c. 30 ft in the field of the wall and 20 ft from a wall’s corner.
d. 30 ft in the field of the wall and 10 ft from a wall’s corner.
Answers: 1-d, 2-b, 3-c, 4-d, 5-c, 6-a, 7-a, 8-a, 9-b, 10-a, 11-c, 12-a, 13-e, 14-c, 15-c, 16-c, 17-d.
713
Drywall interior finish screwed to light-gauge steel furring
sections (see Figure 17.4). If painted (or unpainted) CMU
interior is acceptable, drywall finish is unnecessary.
Vertical reinforcement in CMU back-up wall,
if required for lateral load resistance
Wire anchor, see
Figures 26.17(a)
and 26.18
Termination bar to anchor
flashing to back-up wall
Full bed of
mortar under
first CMU course
Floor slab
Spandrel beam
Rigid insulation
Mortar-capturing device
Flashing
Shelf angle at
spandrel beam
Brick veneer
FIGURE 26.16 Brick veneer with CMU backup.
26.2 BRICK VENEER WITH A CMU OR CONCRETE
BACKUP WALL
Figure 26.16 shows an overall view of a brick veneer wall assembly with a concrete masonry
backup wall. The steel anchors that connect the veneer to the CMU backup wall are twopiece wire anchors. One piece is part of the joint reinforcement embedded in the CMU
walls. See Figure 26.17(a). The other piece fits into this piece and is embedded into the
veneer’s bed joint.
Several other types of anchors used with a concrete masonry backup wall are available,
such as that showns in Figure 26.17(b). Figure 26.17(c) and (d) show typical anchors used
with reinforced-concrete members.
In seismic regions, the use of seismic clips is recommended. A seismic clip engages a continuous wire reinforcement in brick veneer. Both the seismic clip and wire are embedded in
the veneer’s bed joint. A typical seismic clip is shown in Figure 26.18. [See Figure 26.17(d)
714
Horizontal joint
reinforcement
Joint reinforcement
and looped anchor are
prefabricated as one piece
Grout this cell
and the one below
Looped anchor
The slot in this clip engages
into looped anchor and holds
insulation in place,
see Figure 26.18
This anchor fits into the loop and
is embedded into veneer's bed joint
(a) A typical anchor used with CMU back-up walls
(b) An alternative anchor for CMU back-up walls
Concrete wall
Sheet metal dovetail pocket
embedded in reinforced concrete
member. Manufacturers provide
the pocket filled with foam, which
is scraped clean before installing
the dovetail anchor
Anchor with a
seismic clip
Wire
reinforcement
Dovetail end of anchor
engages in pocket and
corrugated part is
embedded in veneer
(c) A typical anchor for concrete back-up wall, beam or column
(d) An alternative anchor for concrete back-up wall, beam or column
FIGURE 26.17 Typical anchors used with CMU and concrete backup walls.
715
PART 2
CMU
Air space
Insulation
Brick veneer
Wire
reinforcement
maximum 3/16 in.
diameter
(Molded plastic)
seismic clip
FIGURE 26.18 A typical seismic clip.
716
CHAPTER 26
See Chapter 31
(and Reference 3)
for roofing details.
See Figure 26.19(b)
for this detail.
FIGURE 26.19 (a) A wall section through a typical multistory reinforced concrete building with
brick veneer and CMU backup wall.
for an alternative seismic clip.] Figures 26.19 to 26.22 show important details of brick
veneer construction and a CMU backup wall.
The shelf angle and lintel angles can be combined into one by increasing the depth
of the spandrel beam down to the level of the window head, Figure 26.23—a strategy
that is commonly used with ribbon windows and continuous brick veneer spandrels,
Figure 26.24.
717
Anchor connects veneer
to CMU back-up wall
Vertical reinforcement in wall (may not
be needed if lateral loads are small)
Moisture barrier coating
on exterior surface of CMU
wall, if needed, see Figure
26.21
Steel dowels from spandrel beam
Drywall
Steel furring section, see Figure 17.4
Rigid foam insulation
(extruded polystyrene or
polyisocyanurate typical)
Anchor connects veneer
to concrete beam
Seal here
Termination bar to anchor
flashing to back-up
Mortar-capturing device
Flashing and
weep holes
Steel weld plate
embedded in
beam
Backer rod and sealant,
see Figure 26.6
Shelf angle
Seal here
Restraint
angles on
both sides of
CMU wall, see
Figure 26.22
Flashing
Treated wood nailer to
anchor window frame
Lintel angle
Drywall
Weep holes
Backer rod and sealant
Ceiling
CMU lintel
Seal here
FIGURE 26.19 (b) Detail of Figure 26.19(a).
718
Insulate and
seal gap
Spandrel beam
Plate embed
Plate embed. Spacing of
embed depends on the load
carried by shelf angle and
concrete strength
Weld here
Space for shims that
extend full height of
vertical leg of shelf angle
Shelf angle
Weld here
Shelf angle
(a) Shelf angle field-welded to embeds in concrete beam
Cast steel wedge insert with foam fill.
The fill is removed before installing the
shelf angle
Cast steel
wedge insert
Washer
Slotted hole allows
field adjustment of
shelf angle
Shelf angle
Space for shims that extend full
height of vertical leg of shelf angle
Shelf angle
(b) Shelf angle bolted to wedge inserts in concrete beam
FIGURE 26.20 Two alternative methods of anchoring a shelf angle to reinforced concrete spandrel beam.
FIGURE 26.21 The exterior surface of a CMU backup wall may be treated with a water-resistant
coating before constructing brick veneer. (Photo by MM.)
719
Restraint
angle
Shelf angle
Restraint
angle
(a) Restraint angles are attached to the bottom of the spandrel
beam. Spacing of restraint angles is a function of lateral load on wall.
Spandrel
beam
Spandrel beam
Dovetail restraint anchor, whose
lower (cylindrical) part is encased in
a plastic tube. The upper part of
the anchor engages in the dovetail
slot. A CMU sash unit is used in
the back-up wall to engage the
tube-encased leg of the anchor in
the block's groove. The groove is
filled with mortar.
Continuous dovetail
slot in spandrel beam
Groove in CMU sash
unit (see Figure 23.5)
Wall reinforcement
(b) Dovetail anchors are an alternative to restraint angles.
Again, spacing of anchors is a function of lateral load on wall.
FIGURE 26.22 Two alternative methods of providing lateral load restraint at the top of a CMU
backup wall. (Photos by MM.)
CMU backup
Cavity insulation
FIGURE 26.23 (Left) With a deep
spandrel beam that extends from
the top of window head in the
lower floor to the sill level of the
window at the upper floor, the
shelf angle also serves as lintel
angle. (Photo by MM.)
Deep beam
Shelf/lintel angle
FIGURE 26.24 (Right) A building
with brick veneer spandrels and
ribbon windows. (Photo by MM.)
720
26.3 BRICK VENEER WITH
A STEEL STUD BACKUP WALL
CHAPTER 26
The construction of brick veneer with a steel stud backup wall differs from that of a CMUbacked wall mainly in the anchors used for connecting the veneer to the backup. Various
types of anchors are available to suit different conditions. The anchor shown in Figure 26.25 is used if the air space does not contain rigid foam insulation so that it is fastened
to steel studs through exterior sheathing.
The anchor shown in Figure 26.26 is used if rigid foam insulation is present in the air
space. The sharp ends of the prongtype anchor pierce into the insulation (not the sheathing)
and transfer lateral load to the studs without compressing the insulation.
Steel stud
Interior drywall
Exterior
sheathing
Anchor with
self-adhering,
self-sealing
tape behind
(a) Anchor (with self-adhering,
self-sealing tape behind, not shown)
Brick veneer
(b) Steel stud and
brick veneer assembly
Anchor
Exterior sheathing
Steel stud
FIGURE 26.25 A typical steel stud and brick veneer assembly without cavity insulation. (Photo by MM.)
Steel stud
Exterior
sheathing
Insulation
Anchor with
self-adhering,
self-sealing
tape behind
(a) Prong-type Anchor
Brick veneer
(b) Steel stud and
brick veneer assembly
FIGURE 26.26 A typical steel stud and brick veneer assembly with outside insulation. (Illustration
courtesy of Hohmann and Barnard, Inc.)
721
PART 2
S TEEL S TUD B ACKUP WALL AS I NFILL
WITHIN THE S TRUCTURAL F RAME
Figure 26.27 shows a detailed section of brick veneer applied to a steel stud backup wall
with the reinforced concrete structural frame. The deflection of the spandrel beam is
accommodated by providing a two-track assembly consisting of a deep-leg track and a normal track, Figure 26.28(a). The upper track of this slip assembly is fastened to the beam.
The studs and the interior drywall are fastened only to the lower track, which allows the
upper track to slide over the lower track.
Bottom track
Seal here
Upper deep-leg track
fastened to beam
Space for beam's deflection.
Fill with fiberglass insulation
Lower track. Studs, interior
drywall and exterior sheathing
fastened to lower track
FIGURE 26.27 Detail of a typical steel stud and brick veneer assembly in a reinforced concrete
structure.
722
Upper (deep-leg) track
Deep-leg
slotted track
Lower track
Stud
(a) Double slip track assembly
(b) Single slotted, slip track assembly
FIGURE 26.28 Two alternative methods of providing a slip-track assembly in a steel stud backup wall (of Figure 26.27). A slotted track
assembly provides a positive connection between the studs and the track.
Alternatively, a single, slotted, deep-leg slip-track assembly may be used. See Figure
26.28(b). The studs are loose fastened to the top track through the slots. The drywall is not
fastened to the slotted track. The slotted track assembly is more economical and also provides a positive connection between the track and the studs.
S TEEL S TUD B ACKUP
OF THE S TRUCTURAL
WALL F ORWARD
F RAME
In low-rise buildings (one or two stories), putting the steel stud backup on the outside of
the structure allows it to cover the structural frame. Thus, the studs are continuous from
the bottom to the top, requiring no shelf angles, Figures 26.29 and 26.30.
Slip connections must be used to connect the studs with the floor or roof so that the
structural frame and the wall can move independently of each other. Two alternative
means of providing slip connections are used, depending on the profile of the studs,
Figure 26.31.
FIGURE 26.29 In a one- or two-story building with steel stud backup wall and steel frame
structure, the studs are generally continuous from the bottom to the top. The vertical continuity
of studs across a floor and (or) roof also helps to reduce their size in resisting the lateral loads.
(Photo by MM.)
723
PART 2
30 ft maximum, see
also Figure 26.5(a)
Continuous studs
from foundation to
the top
Refer to Figure
26.30(b) for the
enlarged version
of this detail
FIGURE 26.30 (a) A typical section through a low-rise (one- or two-story) steel-frame building
with a brick veneer and steel stud backup wall assembly. Brick veneer is continuous from the foundation to the underside of parapet coping.
724
Firestop
Steel deck
Pour stop
Spray-applied
fire protection
Brick
veneer
Steel stud
assembly
Exterior
sheathing
Interior drywall
Ceiling
FIGURE 26.30 (b) Enlarged version of detail at floor level in Figure 26.30(a).
Metal deck with
concrete topping
Pour
stop
Spandrel beam
Slide clip
FIGURE 26.31 Two alternative methods of providing a slip connection between a steel stud backup wall and the floor/roof structure, depending on the profile of studs.
725
PART 2
A brick veneer attached to a steel stud backup wall forward of the structure can also be
used in mid- and high-rise buildings. Two alternative details commonly used for buildings
with ribbon windows and brick spandrels are shown in Figures 26.32 and 26.33.
W EATHER R ESISTANCE
OF A
S TEEL S TUD B ACKUP WALL
Weather resistance of exterior sheathing on steel studs may be accomplished by one of the
following two means:
• Using a membrane that covers the entire sheathing, such as an air-weather retarder
• Using a water-resistant tape on the joints between sheathing panels
Steel angle hanger
FIRESTOP DETAIL
Pourable
firestop
sealant
Impaling
clip
Shelf
angle
Fiberglass insulation
compressed 25 to 30%
Bolted connection between hanger and shelf
angle for field adjustment. Weld hanger and
shelf angle after completing alignment.
Firestop
Brick veneer
Spandrel
beam
Clip angle welded
to beam
Steel angle
hanger
Steel angle brace
Mortar-capturing
device, flashing
and weep holes
Spray-applied fire protection
not shown for sake of clarity
Bent-plate
shelf angle
FIGURE 26.32 Brick spandrel with steel stud backup wall. Steel studs and brick veneer bear on bent-plate shelf angle.
726
Structural steel C-section
Bottom
track for
steel studs
Steel stud anchored to
structural steel C-section
Shelf angle welded to
structural steel C-sections
Structural steel C-section terminates here.
Weld C-section to bent plate pourstop.
Where the lateral loads are low, structural steel
channels may be spaced at two or three times
the spacings of steel studs.
Firestop
Spandrel beam
Structural steel C-section terminates here
bottom track
FIGURE 26.33 (a) Brick spandrel with steel stud backup wall. The shelf angle is hung from structural steel channels and supports only the
brick veneer. See Figure 26.33(b).
727
PART 2
Steel stud anchored
to structural steel
channel
Structural steel
channel
Shelf angle
FIGURE 26.33 (b) Structural frame for brick spandrel with steel stud backup wall. The shelf angle
is hung from vertical structural steel channels and supports only the brick veneer. (Photos by MM.)
Taped joint
FIGURE 26.34 A partially taped
exterior sheathing over steel
studs, photographed while the
taping of sheathing was in
progress. (Photo by MM.)
The use of a continuous membrane conceals the joints between siding panels, making it
more difficult for the masons to locate the studs to which the fasteners must be anchored.
With taped joints, it is easier to locate the studs, Figure 26.34.
26.4 CMU BACKUP VERSUS STEEL STUD BACKUP
A major benefit of a steel stud backup wall in a brick veneer assembly (as compared with
a CMU backup wall) is its lighter weight. For a high-rise building, the lighter wall not
only reduces the size of spandrel beams but also that of the columns and footings, yield728
ing economy in the building’s structure. However, this benefit is accompanied by several
concerns.
Steel studs can deflect considerably before the bending stress in them exceeds their ultimate capacity. Brick veneer, on the other hand, deflects by a very small amount before the
mortar joints open. Open mortar joints weaken the wall and also increase the probability of
leakage, corroding the anchors.
Thus, the steel stud backup and brick veneer assembly performs well only if the stud
wall is sufficiently stiff. To obtain the necessary stiffness, the deflection of studs must be
controlled to a fairly small value. In fact, the design of a steel stud backup wall to resist the
lateral loads is governed not by the strength of studs but by their deflection.
The Brick Industry Association (BIA) recommends that the lateral load deflection of
steel studs, when used as backup for brick veneer assembly, should not exceed
CHAPTER 26
stud span
600
where the stud span is the unsupported height of studs. For example, if the height of studs
(e.g., from the top of the floor to the bottom of the spandrel beam in Figure 26.7) is 10 ft,
the deflection of studs under the lateral load must be less than
110 * 122
600
= 0.2 in.
Increasing the stiffness of studs increases the cost of the assembly. Another concern with
steel stud backup is that the veneer is anchored to the backup only through screws that
engage the threads within a light-gauge stud sheet. Over a period of time, condensation can
corrode the screws and the corresponding holes in studs, making the screws come loose.
Condensation is, therefore, an important concern in a steel stud–backed veneer. A more
serious concern is that the anchor installer will miss the studs.
By comparison with steel studs, anchoring of brick veneer to a CMU backup does not
depend on screws; and hence it is more forgiving. Additionally, the anchors in a CMU
backup wall are embedded in the mortar joints, and if they are made of stainless steel, their
corrosion probability is extremely low.
Another advantage of a CMU backup wall is its inherent stiffness. To obtain a steel stud
backup wall of the same stiffness as a CMU backup wall substantially increases the cost of
the stud backup.
NOTE
Defection of a Steel Stud
Wall Assembly
The design criterion of deflection not exceeding span
divided by 600, suggested by
BIA, is the minimum requirement. For critical buildings, a
more stringent deflection criterion, such as span divided by
720 or span divided by 900, is
recommended by some
experts.
Steel stud manufacturers
generally provide tables for the
selection of their studs to conform to the deflection criteria.
26.5 AESTHETICS OF BRICK VENEER
It is neither possible nor within the scope of this text to illustrate various techniques used
to add visual interest to brick veneer facades. However, a few examples are provided:
• Use of recessed or projected bricks in the wall, Figure 26.35.
• Use of bricks of different colors or combining clay bricks with other masonry materials or cast concrete, Figure 26.36.
• Warping the wall, Figure 26.37.
FIGURE 26.35 Use of recessed or projected bricks with
different hues. The projections must be small so that the
core holes in bricks are not exposed. (Photo by MM.)
729
PART 2
Band appears
as a lintel but
is only decorative
FIGURE 26.36 Use of precast
(white) concrete bands in veneer.
(Photo by MM.)
FIGURE 26.37 Warped brick veneer
used in Frank Gehry’s Peter B. Lewis
Building, Cleveland, Ohio. (Photo by
an architecture student at the
University of Texas at Arlington.)
PRACTICE
QUIZ
18. A typical anchor used with brick veneer and CMU backup wall
assembly consists of a
a. two-piece anchor, of which one is embedded in CMU backup
and the other is embedded in the veneer’s mortar joint.
b. three-piece anchor, of which two are fastened to the CMU
backup and the other is embedded in the veneer’s mortar joint.
c. two-piece anchor, of which one is an integral part of the joint
reinforcement in CMU backup and the other is embedded in
the veneer’s mortar joint.
d. (a) and (b).
e. (a) and (c).
19. When lintel angles and shelf angles are combined in the same angle
in a brick veneer clad building, the angle should be treated as a
a. lintel angle anchored to the structural frame of the building.
b. lintel angle loose-laid over underlying veneer.
c. shelf angle loose-laid over underlying veneer.
d. shelf angle anchored to the structural frame of the building.
20. In general, a CMU-backed brick veneer is more forgiving of
construction and workmanship deficiencies than a steel
stud–backed brick veneer.
a. True
b. False
21. In a brick veneer assembly with a steel stud backup wall, the
design of studs is generally governed by
a. the compressive strength of studs to withstand gravity loads.
b. the shortening of studs to withstand gravity loads.
c. the bending strength of studs to withstand lateral loads.
d. the deflection of studs to withstand lateral loads.
e. any one of the above, depending on the wall.
Answers: 18-e, 19-d, 20-a, 21-d.
26.6 PRECAST CONCRETE (PC) CURTAIN WALL
Unlike brick veneer, which is constructed brick by brick at the construction site, a precast
concrete (PC) curtain wall is panelized construction. The panels are constructed off-site,
under controlled conditions, and transported to the site in ready-to-erect condition, greatly
reducing on-site construction time.
Although the PC curtain wall system is used in all climates, it is particularly favored in
harsh climates, where on-site masonry and concrete construction are problematic due to
freeze hazard and slow curing rate of portland cement. Panelized construction eliminates
730
scaffolding, increasing on-site workers’ safety. Because panel fabrication
can be done in sheltered areas, it can be accomplished uninterrupted, with
a higher degree of quality control.
PC curtain walls are used for almost all building types but more often
are used for mid- to high-rise hospitals, apartments, hotels, parking
garages, and office buildings, Figures 26.38.
PC curtain wall panels are supported on and anchored to the building’s
structural frame and are hoisted in position by cranes. See Figure 26.39(a)
and (b). The panels are fabricated in a precast concrete plant and transported
to a construction site.
The structural design of PC curtain wall panels is generally done by the
panel fabricator to suit the fabrication plant’s setup and resources and to provide an economical product. A typical precast concrete plant generally has
in-house structural engineering expertise.
In a PC curtain wall project, an important role for the architect is to work out
the aesthetic expression of the panels (shapes, size, exterior finishes, etc.). This
should be done in consultation with the precast plant. A great deal of coordination between the architect, engineer of record, general contractor, precast plant,
and erection subcontractor is necessary for a successful PC curtain wall project.
Because of the sculptability of concrete and the assortment of possible finishes of the concrete surface (smooth, abrasive-blasted, acid-etched, etc.), PC
curtain walls lend themselves to a variety of facade treatments. The use of
reveals (aesthetic joints), moldings, and colored concrete further add to the
design variations, Figure 26.40.
PANEL S HAPES
AND
S IZE
Another key design decision is the size, shape, and function of each panel.
These include window wall panels, spandrel panels, and column covers,
Figure 26.41. The panels are generally one floor high, but those spanning
two or (occasionally) three floors may be used.
PC wall panels are generally made as large as possible, limited only by the erection capacity of the crane, transportation limitations, and gravity load delivered
by the panel to the structural frame. For structural reasons, the panels generally
extend from column to column. Smaller panel sizes mean a larger number of
panels, requiring a greater number of support connections, longer erection time,
and, hence, a higher cost. If the scale of large panels is visually unacceptable, false
joints can be incorporated in the panels, as shown in preceding images.
FIGURE 26.38 A typical office building with precast
concrete curtain wall panels. (Photo by MM.)
C ONCRETE S TRENGTH
PC curtain wall panels are removed from the form as soon as possible to allow
rapid turnover and reuse of the formwork. This implies that the 28-day concrete strength should be reasonably high so that when the panel is removed
from the form, it can resist the stresses to which it may be subjected during
the removal and handling processes.
The required concrete strength is also a function of the curtain wall’s
exposure, durability requirements, shape, and size of the panels. Flat panels
may require higher strength (or greater thickness) as compared to ribbed or
profiled panels. Therefore, the strength of concrete must be established in
consultation with the precast plant supplying the panels.
The most commonly used 28-day strength of concrete for PC curtain wall
panels is 5,000 psi. This relatively high strength gives greater durability,
greater resistance to rainwater penetration, and an improved in-service performance. In other words, the panels are better able to resist stresses caused
by the loads, building movement, and volume changes induced by thermal,
creep, and shrinkage effects.
For aesthetic and economic reasons, a panel may use two mixes—a face
(architectural) mix and a backup (structural) mix. In this case, the two mixes
should have nearly equal expansion and contraction coefficients to prevent
undue bowing and warping of the panel. In other words, the strength,
slump, and water-cement ratios of the two mixes should be nearly the same.
Because panels are generally fabricated face down on a flat formwork, the
face mix is placed first followed by the backup mix. The thickness of the face
FIGURE 26.39 (a) A PC panel being unloaded from the
delivery truck for hoisting into position by a crane.
(Photo by MM.)
PC panel
FIGURE 26.39 (b) PC panel of Figure 26.39(a) being
hoisted to its final position. (Photo by MM.)
731
FIGURE 26.40 (a) Lightly abrasive blasted
panels with a great deal of surface detailing.
(Photo by MM.)
FIGURE 26.40 (b) The part of this panel
on the left side of the reveal is lightly
abrasive blasted, and the right side part is
medium abrasive blasted. (Photo by MM.)
FIGURE 26.40 (c) Panel with exposed
aggregate finish. (Photo by MM.)
mix is a function of the aggregate size but should not be less than 1 in. The precaster’s experience should be relied upon in determining the thicknesses and properties of the two mixes.
PANEL T HICKNESS
The thickness of panels is generally governed by the handling (erection) stresses rather than
the stresses caused by in-service loads. A concrete cover on both sides and the two-way reinforcement in a panel generally gives a total of about 3-in. of thickness. Add to this the
Structural
frame
Beam
(a) Window wall panels
Column
(b) Spandrel panels
Spandrel
panel
Structural
frame
Structural
frame
FIGURE 26.41 A few commonly
used panel shapes. Panels should
preferably extend from column to
column so that their dead load
(which is delivered through two supports only) is transferred to the beam
as close to the column as possible
(see Section 26.7).
732
Infill
panel
(c) Spandrel and infill panels. Infill panels
bear on spandrel panels (see Figure 26.46)
and also function as column covers.
(d) Double-height
window wall panels
CHAPTER 26
thickness that will be lost due to surface treatment, such as abrasive blasting and acid etching,
and the total thickness of a PC wall panel cannot be less than 4 in.
However, because panel size is generally maximized, a panel thickness of less than 6 in.
is rare. A thicker panel is not only stronger but is also more durable, is more resistant to
water leakage, and has higher fire resistance. Greater thickness also gives greater heatstorage capacity (Chapter 5), making the panel less susceptible to heat-induced stresses.
M OCK -U P S AMPLE ( S )
For PC curtain wall projects, the architect requires the precast plant to prepare and submit
for approval a sample or samples of color, texture, and finish. The mock-up panels, when
approved, are generally kept at the construction site and become the basis for judgment of
all panels produced by the precast plant.
26.7 CONNECTING THE PC CURTAIN WALL
TO A STRUCTURE
NOTE
The connections of PC curtain wall panels to the building’s structure are among the most
critical items in a PC curtain wall project and are typically designed by the panel fabricator.
Two types of connections are required in each panel:
• Gravity load connections
• Lateral load connection
There should be only two gravity load connections, also referred to as bearing supports,
per panel and should be located as near the columns as possible. The lateral load connections, also referred to as tiebacks, may be as many as needed by structural considerations,
generally two or more per panel, Figure 26.42.
Steel tube embedded in panel for bearing
support, see Figures 26.43 and 26.44
The connection system of a PC
curtain wall resembles that of
brick veneer connection system and is common to all
types of curtain walls. The
shelf angles in brick veneer
provide the gravity load connection, and the anchors
between the veneer and the
backup provide the lateral
load connection.
Hardware embedded in
panel for tie-back connection
Leveling shims between bearing
plate and panel support
Bearing plate embedded
in spandrel beam
FLOOR-TO-FLOOR SOLID
(OR WINDOW WALL) PANEL
Hardware embedded in panel
for tie-back connection
Steel tube or wide-flange section embedded in panel for bearing support
(see Figure 26.44). While the section shows bearing support above beam,
it can also be placed in a block-out (pocket) in the beam, which is filled
with concrete after making the connection
Steel tube, wide flange section
or an angle embedded in panel
for bearing support
Leveling shims under support
Bearing plate embedded
in spandrel beam
Tie-back connection, see
Figures 26.44 and 26.45
FIGURE 26.42 Support connections for a typical floor-to-floor curtain wall panel.
733
PART 2
Steel tube
Leveling bolt
Leveling nut welded to tube
Bearing plate
Spandrel beam
(a) Detail section showing bearing support of panel
(c) Steel tube embedment
viewed from the top
Leveling nut welded to
the bottom of tube
(b) Steel tube embedment viewed from the bottom
FIGURE 26.43 Leveling nut in a steel tube used for bearing support. (Photo by MM at a precast
plant.)
B EARING S UPPORTS
A commonly used bearing support for the floor-to-floor panels is provided through a section of steel tube, a part of which is embedded in the panel and a part of which projects out
of the panel. The projecting part rests on the (steel angle) bearing plate embedded at the
edge of the spandrel beam. Dimensional irregularities, both in the panel and in the structure, require the use of leveling shims (or bolts) under bearing supports during erection.
After the panels have been leveled, the bearing supports are welded to the bearing plate. The
bearing support system is designed to allow the panel to move
within its own plane so that the panel is not subjected to
stresses induced by temperature, shrinkage, and creep effects.
In place of leveling shims in a bearing support, a leveling
bolt is often used, Figure 26.43. The choice between the
shims and the bolt is generally left to the preference of the
Bearing support
using W-section
precast manufacturer and the erector. Alternatives to the
use of steel tube for bearing supports are steel angles or a
wide-flange (I-) section, Figure 26.44.
Spandrel beam
Tie back connection
Shims under support
FIGURE 26.44 Wide-flange section used as bearing support in a PC panel.
(Photo by MM.)
734
T IEBACKS
A lateral load connection (tieback) is designed to resist horizontal forces on the panel from wind and/or earthquake and
due to the eccentricity of panel bearing. Therefore, it must be
able to resist tension and compression perpendicular to the
plane of the panel.
A tieback is designed to allow movement within the
plane of the panel. The connection must, however, permit
CHAPTER 26
Steel tube embedded into
panel for bearing support
Leveling shims
Coiled ferrule
Steel angle bearing
plate embedded in beam
Coiled ferrule embedded in beam
Spandrel beam
Threaded rod and nut
Clip angle with
slotted holes
Anchor embedded in panel
FIGURE 26.45 A typical tieback
connection that allows three-way
field adjustment during panel erection in addition to in-service vertical
deflection of spandrel beam and thermal expansion/contraction of panel.
adjustment in all three principal directions during erection. A typical tieback is shown in
Figure 26.45 (see also Figure 26.44).
S UPPORT S YSTEMS
FOR
S PANDREL PANELS
AND
I NFILL PANELS
Support systems for a curtain wall consisting of spandrel and infill panels are shown in
Figure 26.46; see also Figure 26.41(c).
PANELS
AND
S TEEL F RAME S TRUCTURE
PC wall panels, which create eccentric loading on the spandrel beams, create torsion in the
beams. Due to the lower torsional resistance of wide-flange steel beams, PC panels used with
a steel frame structure are generally designed to span from column to column and made to
bear directly on them. Tiebacks, however, are connected to the spandrel beams. (Note that
the rotation of the spandrel beam caused by the eccentricity of panel bearing is partially
balanced by reverse rotation caused by the the floor’s gravity load on the spandrel beam.)
C LEARANCE
OF
PANELS
FROM THE
S TRUCTURAL F RAME
The Precast/Prestressed Concrete Institute (PCI) recommends a minimum horizontal
clearance of 2 in. of precast panels from the building’s structural frame.
26.8 BRICK AND STONE-FACED PC CURTAIN WALL
PC curtain wall panels may be faced with thin (clay) bricks at the time of casting the panels. Generally, 34 - to 1-in-thick bricks are used. They are available in various shapes, Figure 26.47. The bricks are placed in the desired pattern in the form, and the concrete is
735
PART 2
Embed for tie-back connection
Embed for bearing support
Embeds for tieback connection
Embed for tie-back connection
Stretcher
Embed for
bearing support
Embeds for tieback connection
Three-side
corner
Line of top of floor on which
the panel is to be supported
(a) A PC spandrel panel being
brought into its final position.
Corner
(b) Support connections for an
infill panel bearing on a spandrel
panel, see Figure 26.41(c)
Edge Corner
FIGURE 26.46 Support connections for: (a) a spandrel panel, (b) a column cover bearing on
spandrel panels.
FIGURE 26.47 A few thin clay brick
shapes available.
FIGURE 26.48 Rubber template form
liner used with thin brick-faced panels.
736
placed over them. To prevent the bricks from shifting during the placing operation, a rubber template is used, within which the bricks are placed, Figure 26.48. The template aligns
the bricks and allows the concrete to simulate the mortar joints.
In well-designed and well-fabricated panels, it is generally difficult to distinguish
between a site-constructed brick veneer wall and a brick-faced PC curtain wall. Brick-faced
panels have the same advantages as other PC curtain wall panels—that is, no on-site construction and no scaffolding.
Thin bricks need to be far more dimensionally uniform than full-size bricks. With
full-size bricks, dimensional nonuniformity is compensated by varying the mortar
thickness.
Because clay bricks expand by absorbing moisture from the atmosphere (moisture
expansion), thin bricks should be allowed to season for a few weeks at the precaster’s plant
before being used. This reduces their inherent incompatibility with concrete, which shrinks
on drying.
Although moisture expansion and drying shrinkage are the major causes of incompatibilities between bricks and concrete, other differences between the two materials, such as
the coefficient of thermal expansion and the modulus of elasticity, must be considered.
Because of these differences, a brick-faced concrete panel is subject to bowing due to differential expansion and contraction of the face and the backup.
Bowing can be reduced by increasing the stiffness of the panel. Using two layers of reinforcement is encouraged when the thickness of the panel permits. Additionally, some precasters use reverse curvature in the panels.
The bond between concrete and bricks is obviously very important for a brick-faced
concrete wall panel. The back surface of bricks used in brick-faced panels should contain
grooves, ribs, or dovetail slots to develop an adequate bond. The bond between concrete
and brick is measured through a shear strength test. The architect should obtain these
results from the brick manufacturer before specifying them for use.
The bond between concrete and bricks is also a function of how absorptive the bricks
are. Bricks with excessively high or excessively low water absorption give a poor bond.
Bricks with high water absorption are subjected to freeze-thaw damage.
CHAPTER 26
S TONE V ENEER –FACED PC PANELS
PC curtain wall panels can also be faced with (natural) stone veneer. The thickness of the
veneer varies with the type of stone and the face dimensions of the veneer units. Granite
and marble veneers are recommended to be at least 1 41 in. (3 cm) thick. Limestone veneer
should be at least 2 in. thick.
The face dimensions of individual veneer units are generally limited to 25 ft2 for granite
and 15 ft2 for marble or limestone. Thus, a typical PC curtain wall panel has several veneer
units anchored to it.
The veneer is anchored to the concrete panel using stainless steel flexible dowels, whose
3
diameter varies from 16
to 58 in. Two dowel shapes are commonly used—a U-shaped
(hairpin) dowel and a pair of cross-stitch dowels, Figure 26.49. The dowels are inserted in
1
the holes drilled in the veneer. The dowel holes, which are 16
to 81 in. larger in diameter
than the diameter of the dowels, are filled with epoxy or an elastic, fast-curing silicone
sealant. Unfilled holes will allow water to seep in, leading to staining of the veneer and
freeze-thaw damage.
Because the dowels are thin and flexible, they allow relative movement between the
veneer and the backup. To further improve their flexibility, rubber washers are used with
the dowels at the interface of the veneer and the backup.
The depth of anchor in the veneer is nearly half the veneer thickness. Their anchorage
into concrete varies, depending on the type of stone and the loads imposed on the panel.
There should be no bond between stone veneer and and the backup concrete to prevent
bowing of the panel and cracking and staining of the veneer. To prevent the bond, a bond
breaker is used between the veneer and the backup. The bond breaker is either a 6- to 10mil-thick polyethylene sheet or a 81 - to 14 -in.-thick compressible, closed-cell polyethylene
foam board. Foam board is preferred because it gives better movement capability with an
uneven stone surface.
A PC curtain wall panel may be either fully veneered with stone or the veneer may be
used only as an accent or feature strip on a part of the panel.
OTHER F ORM L INERS
Because concrete is a moldable material, several geometric and textured patterns can be
embossed on panel surface using form liners. An architect can select from a variety of standard
form liners available or have them specially manufactured for a large project (Section 19.4).
Pair of cross-stitched dowels
Hairpin shape dowel
Concrete back-up
Rubber washer
Bond breaker
Fill space between dowel
and hole with epoxy or
silicone sealant.
Stone veneer
FIGURE 26.49 Two commonly used dowel anchors.
737
PART 2
26.9 DETAILING A PC CURTAIN WALL
A typical PC curtain wall is backed by an infill steel stud wall. The stud wall provides
the interior finish and includes the insulation and electrical and other utility lines.
Because the backup wall is not subjected to wind loads, it needs to be designed only for
incidental lateral loads from the building’s interior (generally 5 psf ). Therefore, a fairly
lightweight backup wall is adequate. This contrasts with a backup stud wall in a brick
veneer wall, which must be designed to resist wind loads and be sufficiently stiff to have
a relatively small deflection.
Figure 26.50 shows a representative detail of a PC curtain wall with a steel stud backup
wall. The space between the panels and the backup wall may be filled with rigid insulation,
if needed.
J OINTS
BETWEEN
PANELS
Detailing the joints between panels is also a critical aspect of a PC curtain wall project. A minimum joint width of 1 in. between panels is generally recommended. Although a single-stage
joint is commonly used, the preferred method is to use a two-stage joint system, consisting
PC curtain wall panel
with punched window
Drywall interior finish
over vapor retarder
Steel stud wall with fiberglass
insulation in stud cavities
Seal here
Firestop
Rigid insulation,
if needed
Spandrel
beam
Two-stage
joint seal
Double deep leg slip
track assembly
Treated wood nailer
for fastening window
Ceiling
Drywall interior finish
over vapor retarder
Steel stud wall with fiberglass
insulation in stud cavities
FIGURE 26.50 A typical PC curtain wall (schematic) detail.
738
OUTSIDE
INSIDE
INSIDE
Provide weep holes
in the outer seal
OUTSIDE
INSIDE
OUTSIDE
(c) Two-stage vertical joint
Both seals applied from the outside
(a) Single-stage horizontal joint
(b) Two-stage horizontal joint. Both seals applied from the outside
FIGURE 26.51 Treatment of joints between PC curtain wall panels.
of a pair of backer rod and sealant bead combination. One backer rod and sealant bead
combination is placed toward the outer surface of the joint and the other is placed toward the
inner surface, Figure 26.51.
The outer seal provides a weather barrier and contains weep holes. The inner seal is continuous without any openings and is meant to provide an air barrier. The air barrier must
extend continuously over a panel and across the joint between panels. The provision of the air
barrier and the openings in the exterior seal makes the two-stage joint system function as a
rain screen (Chapter 25).
Both inner and outer seals should be applied from the outside to avoid discontinuities at
the spandrel beams and floor slabs. This requires a deep-stem roller to push the backer rod
deep into the joint and a long-nozzle sealant gun.
I NSULATED , S ANDWICHED PANELS
PC curtain wall panels with rigid plastic foam insulation sandwiched between two layers of
concrete may be used in cold regions. A sandwich panel consists of an outer layer of concrete and an inner layer of concrete, in which both layers are connected together with ties
through an intermediate layer of rigid plastic foam insulation.
The outer layer is a nonstructural layer, whereas the inner layer is designed to carry the
entire load and transfer it to the structural frame. The panel is fabricated by first casting
the concrete for the nonstructural layer. This is followed by embedding the ties and placing
the insulation boards over the ties. The insulation is provided with holes so that the ties project above the insulation and are embedded in the concrete that is cast above the insulation.
PRACTICE
22. The strength of concrete used in precast concrete curtain walls is
generally
a. greater than or equal to 3,000 psi.
b. greater than or equal to 4,000 psi.
c. greater than or equal to 5,000 psi.
23. Precast concrete curtain wall panels are generally
a. cast on the construction site.
b. fabricated by a readymix concrete plant and transported to the
construction site.
c. (a) or (b).
QUIZ
24. The number of bearing supports in a precast concrete curtain wall
panel must be
a. one.
b. two.
c. three.
d. four.
e. between three and six.
25. The structural design of precast concrete curtain wall panels is
generally the responsibility of the
a. structural engineer who designs the structural frame of the
building in which the panels are to be used.
b. structural engineer retained by the panel fabricator.
c. structural engineer retained by the general contractor of the
building.
d. structural engineer specially retained by the owner.
739
PRACTICE
QUIZ
( Continued )
28. A bond break such as a polyethylene sheet membrane is generally
used between the concrete and bricks in a brick-faced precast
concrete curtain wall panel.
a. True
b. False
26. During the erection of precast concrete curtain wall panels, the
panels are leveled. The leveling of the panels is provided in the
a. panels’ bearing supports.
b. panels’ tieback connections.
c. (a) or (b).
d. (a) and (b).
29. The connection between natural stone facing and the backup
concrete in a stone-faced precast concrete curtain wall panel is
obtained by
a. The roughness of the stone surface that is in contact with
concrete.
b. nonmoving steel dowels.
c. flexible steel dowels.
d. any one of the above.
27. The bricks used in brick-faced concrete curtain wall panels are
generally
a. of the same thickness as those used in brick veneer
construction.
b. thicker than those used in brick veneer construction.
c. thinner than those used in brick veneer construction.
d. any one of the above, depending on the building.
Answers: 22-c, 23-d, 24-b, 25-b, 26-a, 27-c, 28-b, 29-c.
26.10 GLASS FIBER–REINFORCED CONCRETE
(GFRC) CURTAIN WALL
As the name implies, glass fiber–reinforced concrete (GFRC) is a type of concrete whose
ingredients are portland cement, sand, glass fibers, and water. Glass fibers provide tensile
strength to concrete. Unlike a precast concrete panel, which is reinforced with steel bars, a
GFRC panel does not require steel reinforcing.
The fibers are 1 to 2 in. long and are thoroughly mixed and randomly dispersed in the
mix. The random and uniform distribution of fibers not only provides tensile strength, but
also gives toughness and impact resistance to a GFRC panel. Because normal glass fibers are
adversely affected by wet portland cement (due to the presence of alkalies in portland
cement), the fibers used in a GFRC mix are alkali-resistant (AR) glass fibers.
GFRC S KIN
AND
S TEEL F RAME
A GFRC curtain wall panel consists of three main components:
• GFRC skin
• Light-gauge steel backup frame
• Anchors that connect the skin to the steel backup frame
Of these three components, only the skin is made of GFRC, which is generally 12 - to 34 in.-thick. The skin is anchored to a frame consisting of light-gauge (galvanized) steel members, Figure 26.52. In this combination, the GFRC skin transfers the loads to the frame,
which, in turn, transfers the loads to the building’s structure. The size and spacing of backup
frame members depends on the overall size of the panel and the loads to which it is subjected.
Reveal (aesthetic joint)
FIGURE 26.52 (a) The front of a large GFRC panel after light abrasive blasting. It is being lifted for
storage in the fabricator’s yard. (Photo by MM.)
740
F LEX A NCHORS
CHAPTER 26
The skin is hung 2 in. (or more) away from the face of the frame using bar anchors. The
gap between the skin and the frame is essential because it allows differential movement
between the skin and the frame, particularly during the period when the fresh concrete in
the skin shrinks as water evaporates.
The anchors are generally 38 -in.-diameter steel bars, bent into an L-shape. To provide
corrosion resistance, cadmium-plated steel is generally used for the anchors. One end of an
anchor is welded to the frame, and the other end is embedded in the skin. The skin is thickened around the anchor embedment. The thickened portion of the skin is referred to as a
bonding pad, Figure 26.53.
The purpose of the anchors is to transfer both gravity and lateral loads from the skin to the
frame. In doing so, the anchors must be fairly rigid in the plane perpendicular to the panel;
that is, they should be able to transfer the loads without any deformation in the anchors.
The GRFC skin includes a
corner return that provides
a means of forming sealed
joints between panels.
A minimum 2 in. return is
required. A larger return
may be needed for a twostage joint between panels.
GFRC skin
Flex
anchor
Reveal (aesthetic joint)
Bonding pad
Vertical frame member
PLAN OF AN L-SHAPED GFRC PANEL
FIGURE 26.52 (b) The side and
back of an L-shaped GFRC panel
showing the supporting steel frame.
(Photos by MM.)
741
GFRC skin
Flex anchor
Bonding pad
2 in.
minimum
gap between
frame and skin
Bonding pad,
see Figure 26.60
Flex
anchor
Anchor
welded here
FIGURE 26.53 Bonding pads and flex anchors. (Photo by MM.)
Frame member
FIGURE 26.54 Flexibility of flex anchors.
However, the skin will experience in-plane dimensional changes due to moisture and
temperature effects. The anchor must therefore have sufficient flexibility to allow these
changes to occur without excessively stressing the skin. One way of achieving this goal is
to flare the anchor away from the frame and to weld it to the frame member at the far
end, Figure 26.54. The term flex anchor underscores the importance of anchor flexibility.
PANEL S HAPES
Like the precast concrete curtain wall panels, GFRC curtain wall panels can be made into
different shapes, depending on the design of the building’s facade. The most commonly
used panels are floor-to-floor solid panels (Figure 26.52), and window wall panels, Figure 26.55 and spandrel panels. A spandrel panel is essentially a solid panel of smaller
height. Because the panels can be configured in several ways for a given facade, the architect must work with the GFRC fabricator before finalizing panel shapes.
2 in. minimum gap between
frame and skin
Opening
for window
Horizontal frame member
Vertical frame
member
GFRC
skin
Horizontal frame
member
SECTION THROUGH A WINDOW WALL PANEL
(Anchors not shown)
FIGURE 26.55 The front and back of a typical window wall panel. (Photo by MM.)
742
26.11 FABRICATION OF GFRC PANELS
CHAPTER 26
Figures 26.56 to 26.60 show the six-step process of fabricating a GFRC panel.
• Preparing the Mold: The mold must be fabricated to the required shape, Figure 26.56.
The mold generally consists of plywood, but other materials, such as steel or plastics,
may be used. A form-release compound is applied to the mold before applying the
GFRC mix to facilitate the panel’s removal from the mold.
• Applying the Mist Coat: Before GFRC mix is sprayed on the panel, a thin cementsand slurry coat, referred to as a mist coat, is sprayed on the mold, Figure 26.57.
Because the mist coat does not contain any glass fibers, it gives a smooth, even surface to the panel. The thickness of the mist coat is a function of the finish the panel
face is to receive. If the panel face is to be lightly abrasive-blasted, a 18 -in.-thick mist
coat is adequate.
• Applying the GFRC Mix: Soon after the mist coat is applied, GFRC mix is sprayed on
the mold. See Figure 26.58(a). GFRC mix consists of (white) portland cement and
sand slurry mixed with about 5% (by weight) of glass fibers. Because air may be
trapped in the mix during spraying, the mix is consolidated after completing the spray
application by rolling, tamping, or troweling, Figure 26.58(b).
• Frame Placement: After the GFRC spray is completed, the steel backup frame is
placed against the skin, leaving the required distance between the skin and the
frame, Figure 26.59.
• Bonding Pads: Finally, bonding pads are formed at each anchor using the same mix as
that used for the skin, Figure 26.60.
• Removing the Panel from the Mold and Curing: The panel (skin and frame) is generally
removed from the mold 24 h after casting and subsequently cured for a number of
days. Because the panel has not yet gained sufficient strength, special care is needed
during the panel’s removal.
Plastic channel to form a reveal.
The channel is removed after the
skin has gained sufficient strength.
FIGURE 26.56 The mold of a roof cornice panel.
FIGURE 26.57 Application of mist coat. (Photo by MM.)
743
FIGURE 26.58 (a) Spraying GFRC mix over the mist coat. Photo by MM. (b) Consolidating GFRC mix using a roller around bends, edges and
corners. (Photo by MM.)
Frame
GFRC skin
FIGURE 26.59 Placing a frame
against the skin. (Photo by MM.)
FIGURE 26.60 Making of a bonding
pad (see also Figure 26.53). (Photos
by MM.)
S URFACE F INISHES
ON
GFRC PANELS
The standard finish on a GFRC panel is a light abrasive-blasted finish to remove the
smoothness of the surface obtained from the mist coat. However, a GFRC panel can also be
given an exposed aggregate finish, which results in a surface similar to that of a precast
concrete panel.
To obtain an exposed aggregate finish, the mist coat is replaced by a concrete layer, referred
3
to as a face mix. The thickness of the face mix is about 8 in., and the aggregate used in
3
1
the face mix is between 16 in. and 4 in. The exposure of aggregate is obtained by abrasive
blasting or acid etching.
744
26.12 DETAILING A GFRC CURTAIN WALL
CHAPTER 26
A GFRC panel is connected to the building’s structure in a system similar to that of a precast concrete panel. In other words, a GFRC panel requires two bearing connections and
two or more tieback connections. However, because GFRC panels are much lighter than
the precast concrete panels, their connection hardware is lighter.
As with precast concrete curtain walls, the structural design of panels and their support
connections is generally the responsibility of panel fabricator. Figures 26.61 and 26.62
Double track
Structural steel tube
Structural steel angle with holes
for leveling bolt provides bearing
support
Structural steel angle with leveling nut
(welded to structural steel tube)
provides bearing support
Ferrule welded to steel tube
provides tie-back connection
Structural
steel tube
Light-gauge
steel members
(a) Back-up frame for GFRC
spandrel panel
Structural steel angle
for bearing support
Leveling bolt
Leveling
nut
This frame shows the use of double
tracks at the top and bottom of the
panel. With the use of diagonal braces,
it may be possible to use only single
tracks. Because frame members are
welded together, a minimum thickness
of 16-gauge is required of light-gauge
frame members.
GFRC skin
Block-out in
spandrel beam,
filled with concrete
after making
connections
Tie-back connection
(b) Section showing connection of GFRC
spandrel panel to building's structure
FIGURE 26.61 Schematic details of bearing and tieback connections in a spandrel GFRC panel (see also Figures 26.62 and 26.63).
745
PART 2
show two alternative schematics for the connection of a GFRC spandrel panel to the building’s structure.
Figure 26.63 shows a typical GFRC curtain wall detail. Because GFRC skin is thin,
some form of water drainage system from behind the skin should be incorporated in the
panels. Additionally, the space between the GFRC skin and the panel frame should be
freely ventilated to prevent the condensation of water vapor. This is generally not a requirement in precast concrete curtain walls. A two-way joint sealant system may be used at panel
junctions similar to that for PC curtain walls (Figures 26.50 and 26.51).
Structural steel tube with holes
for leveling bolt provides bearing
support
Structural steel angle with
holes for leveling bolt provides
bearing support
with holes for leveling
bolt provides bearing
support
Light-gauge
steel members
(a) Back-up frame for GFRC
spandrel panel
Leveling bolt
Steel tube within frame
6 in. long section of steel tube
welded to pour stop
Leveling
nut
This frame shows the use of double
tracks at the top and bottom of the
panel. With the use of diagonal braces,
it may be possible to use only single
tracks. Because frame members are
welded together, a minimum thickness
of 16-gauge is required of light-gauge
frame members.
GFRC skin
Tie-back connection
(b) Section showing connection of GFRC
spandrel panel to building's structure
FIGURE 26.62 Schematic details of bearing supports and tieback connections in a spandrel GFRC panel (see also Figures 26.61
and 26.63).
746
CHAPTER 26
Window assembly supported on frame
Aluminum sill
flashing
GFRC
skin
Outer surface
of GFRC frame
Extruded aluminum interior sill
Aluminum foil-backed rigid mineral
wool insulation with taped joints
Gypsum board on 2-1/2 in. steel studs
(or on furring strips over frame members)
Gap between
GFRC skin
and frame
Gypsum board
Aluminum foil-backed rigid mineral
wool insulation with taped joints
Continuous
drainage to
weep holes
Drip
groove
Spray-applied fire protection
not shown for clarity
Ceiling
Sealant
and backer rod
FIGURE 26.63 Schematic detail of an exterior wall with GFRC spandrel panels and ribbon
windows.
26.13 PREFABRICATED BRICK CURTAIN WALL
Prefabricated brick panels using full-thickness bricks can also be used as curtain wall panels.
The facade of a building with prefabricated brick panels looks similar to that of a building
with site-constructed brick veneer. In a facade with prefabricated brick panels, however, the
exterior soffit can also be of bricks, giving an all-brick appearance.
Figure 26.64 shows a completed building with prefabricated exterior brick panels. The
panels are L-shaped so that the wall and the spandrel and soffit elements are integrated into
one panel. Figure 26.65 shows the details and various stages of erection of the panels.
Brick panels are constructed in the masonry contractor’s fabrication yard (or indoor
plant) and transported to the site. They are reinforced in both directions. Reinforcement in
one direction is provided by epoxy-coated steel bars placed into the core holes of bricks.
The core holes are filled with portland cement–sand grout. In the other direction, galvanized steel joint reinforcement placed within the bed joints of panels is used.
In addition to reinforcing bars and joint reinforcement, a brick curtain wall panel generally requires two structural steel frames integrated into the brick panel to provide bearing
747
Panel with brick
spandrel and soffit
Spandrel
Soffit
FIGURE 26.64 A building with prefabricated brick
panels. (Photo courtesy of Dee Brown, Inc.)
FIGURE 26.65 Erection of prefabricated brick panels in the building
of Figure 26.64. (Photo courtesy of Dee Brown, Inc.)
Lifting frame
Lifting frame
FIGURE 26.66 A close-up of the
prefabricated brick panel used in the
building shown in Figure 26.64.
(Photo courtesy of Dee Brown, Inc.)
supports and tieback connections. The details of the structural frame, used in the panels of
the building of Figure 26.64, are shown in Figures 26.66 and 26.67.
A steel stud backup wall incorporating insulation, vapor barrier, and drywall is required
with prefabricated brick curtain wall. Additionally, some means must be provided for the
drainage of water from behind the panel.
PRACTICE
QUIZ
30. The term GFRC is an acronym for
a. glass fiber–reinforced concrete.
b. glass fiber–reinforced cement.
c. glass fiber–restrained concrete.
d. glass fiber–restrained cement.
31. A GFRC curtain wall panel consists of
a. a GFRC skin.
b. a light-gauge steel frame.
748
c. anchors.
d. all the above.
e. (a) and (b).
32. The GFRC skin is typically
a. 2 to 3 in. thick.
1
1
b. 12 to3 2 2 in. thick.
c. 1 to 2 in. thick.
1
3
d. 2 to 4 in. thick.
e. None of the above.
CHAPTER 26
FIGURE 26.67 Shop drawings of the prefabricated brick panel used in the building of
Figure 26.64. (Illustration courtesy of Dee Brown, Inc.)
PRACTICE
34. The anchors used in GFRC panels are typically
a. two-piece anchors.
b. one-piece anchors.
c. either (a) or (b), depending on the thickness of GFRC skin.
d. either (a) or (b), depending on the lateral loads to which the
panel is subjected.
35. The GFRC skin is obtained by
a. casting the GFRC mix in a mold similar to casting a precast
concrete member.
( Continued )
b. applying the mix with a trowel.
c. spraying the mix over a mold.
d. any of the above, depending on the panel fabricator.
36. GFRC curtain wall panels are generally lighter than the
corresponding precast concrete curtain wall panels.
a. True
b. False
37. In prefabricated brick curtain wall panels, the bricks used are
a. generally of the same thickness as those used in brick veneer
construction.
b. generally thicker than those used in brick veneer construction.
c. generally thinner than those used in brick veneer construction.
38. Prefabricated brick curtain wall panels are generally fabricated
a. in a brick-manufacturing plant.
b. in a masonry contractor’s fabrication yard.
c. in a precast concrete fabricator’s plant.
d. at the construction site.
Answers: 30-a, 31-d, 32-d, 33-a, 34-b, 35-c, 36-a, 37-a, 38-b.
33. The glass fibers used in GFRC skin are referred to as AR fibers. The
term AR is an acronym for
a. alkali resistant.
b. acid resistant.
c. alumina resistant.
d. aluminum reinforced.
QUIZ
749
REVIEW QUESTIONS
1. Using sketches and notes, explain the adjustability requirements of anchors used in a brick veneer wall assembly.
2. Using sketches and notes, explain the functions of a shelf angle and a lintel angle in a brick veneer assembly.
3. With the help of sketches and notes, explain various ways by which weep holes can be provided in a brick veneer
assembly.
4. Discuss the pros and cons of using a CMU backup wall versus a steel stud backup wall in a brick veneer wall
assembly.
5. With the help of sketches and notes, explain the support system of a precast concrete curtain wall panel.
6. With respect to a GFRC panel, explain: (a) bonding pad and (b) flex anchor.
SELECTED WEB SITES
Brick Industry Association, BIA (www.bia.org)
International Masonry Institute, IMI (www.imiweb.org).
Precast/Prestressed Concrete Institute, PCI (www.pci.org)
Magazine of Masonry Construction (www.masonryconstruction.com)
FURTHER READING
1. American Concrete Institute (ACI). “Tilt-Up Concrete Structures,” Manual of Concrete Practice.
2. Brick Industry Association (BIA). Technical Notes on Brick Construction.
3. Brock, Linda: Designing the Exterior Wall, New York: John Wiley & Sons, 2005.
4. Canadian Mortgage and Housing Corporation (CMHC). Architectural Precast Concrete Walls—Best Practice Guide,
2002.
5. Precast/Prestressed Concrete Institute (PCI). Architectural Precast Concrete. 1989.
6. Precast/Prestressed Concrete Institute (PCI). Recommended Practice for Glass Fiber Reinforced Panels.
7. Tilt-Up Concrete Association (TCA) and American Concrete Institute (ACI). The Tilt-Up Design and Construction
Manual.
REFERENCES
1. American Concrete Institute: Building Code Requirements and Commentary for Masonry Structures and
Specifications for Masonry Structures and Related Commentaries, ACI530/530.1.
2. Brick Industry Association (BIA): “Brick Veneer Steel Stud Walls,” Technical Notes on Brick Construction (28B).
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MATERIALS AND SYSTEMS

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